Working in a group blender project
Version control for blender
There is no special version control system for blender. Your three main choices are git, Mercurial, and SVN.
While I have used git for blender projects and it works (here is a game that was created in a group and was version controlled in git) it is not the best suited because git does not handle binary files, think images and blend files. There is an addon that integrates git in to blender, and let you see and save versions of your file.
SVN is svn and you need a server set up to run that. (The Blender institute has used SVN for their open movie projects).
Mercurial (while I personally have not used it) is best suite to use for Blender. It has the simplicity of git, and (somehow) it can diff binary files.
CG cookie has a good video about setting up version control for blender.
Project Structure
File linking in blender is a pain, but it is the only way to work together in a group.
Say you have one main file, then you will link in the assets that are all separate files. Being separate files enables each person to work on a different piece of the whole at the same time.